I'm putting controls on a vertical mill that will be run via EMC2. From my 
research I've realized 
that I have two choices: the PID loop can be on the DC-driver board or it can 
be within EMC2 with 
EMC2 reading the encoder and outputting a analog value.

It seems there would be less things to go wrong if PID is on the DC-driver 
board.  On the other 
hand, if EMC2 does the control, reading the encoder, spitting out an 
appropriate DC-voltage value, 
EMC2 can do the tuning and could also do "multi-axis-coordination". I'm 
defining multi-axis 
coordination as optimizing a straight line when there is motion on two or more 
axis(there may be a 
more standard term for this?). This provides less aliasing (stair steps) than 
with 
direction-and-step methodology.

I'm also thinking that I might later decide to add a linear encoder to the 
table and might want to 
do a nested PID (actually - just an 'I' outside loop that could actually update 
backlash in real-time)

I am new to EMC2, but I have a background in embedded micro-controllers outside 
of machining and 
have designed and built both analog and digital temperature PID loops.

Any and all feedback on this is welcome - also feel free to call (or ask me to 
call you)..





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Karl Schmidt                         EMail [EMAIL PROTECTED]
Transtronics, Inc.                     WEB http://xtronics.com
3209 West 9th Street                    Ph (785) 841-3089
Lawrence, KS 66049                     FAX (785) 841-0434

"Give me four parameters and I can fit an elephant;
Give me five and I can wag its tail."
(The source of the above quote?? Variants have been
attributed to C.F. Gauss, Niels Bohr, Lord Kelvin, Enrico Fermi.)

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